Scalability and other issues begin to arise as conventional communications networks become larger and larger, e.g., comprising more and more nodes. In networks comprising a single Autonomous System (AS) domain (e.g., depicted below in FIG. 1), each node must be aware of the positional relationships (i.e., adjacencies) of all other nodes, such that all nodes may build a topological map of the network. Nodes may learn about one another's adjacencies by flooding link-state information throughout the network according to one or more interior gateway protocols (IGPs), e.g., open shortest path first (OSPF), intermediate system (IS) to IS (IS-IS), etc. Specifically, nodes engaging in IGPs may distribute their own link state advertisements (LSAs) describing their own adjacencies to all their neighboring nodes, which may forward the received LSAs to all their neighboring nodes (except the node from which the LSA was received). This may allow the LSA to be distributed throughout the network such that all network nodes become aware of one another's adjacencies, thereby allowing the various nodes to build topology tables (e.g., link state databases (LSDBs)). LSAs may be flooded upon network initialization as well as whenever a network adjacency changes (e.g., a node is added/removed, a node/link fails, etc.). Consequently, as more nodes are added to a network, link state distributions may begin to consume more and more network resources (e.g., bandwidth, processing, etc.), and consequently become more cumbersome and time-consuming.
The primary prior art technique for addressing scalability and performance issues in large networks is to define smaller local areas of IGP (e.g., open shortest path first (OSPF) areas, intermediate system (IS) to IS (IS-IS) areas, etc.) in an attempt to reduce the number of LSAs that are flooded throughout the network This technique (e.g., depicted below in FIG. 2) has been described by various publications, such as the Internet Engineering Task Force (IETF) publication request for comments (RFC) 2328 entitled “OSPF Version 2” (describing OSPF areas in an AS domain) and IETF publication RFC 1142 entitled “Open Systems Interconnection (OSI) IS-IS Intra-domain Routing Protocol” (describing IS-IS areas in an AS domain). Specifically, each OSPF/IS-IS area comprises a number of interconnected routers, including both area border routers (ABRs) and internal routers. ABRs may be distinguished from internal routers in that ABRs may be connected to external nodes (e.g., ABRs in other OSPF/IS-IS domains), while internal routers may be connected only to other nodes within the OSPF/IS-IS domain (e.g., not connected to any routers outside the OSPF/IS-IS domain). In most applications, the ABRs and internal routers will execute a normal link state distribution (e.g., according to an IGP) within their respective local OSPF/IS-IS areas, thereby allowing the ABRs to collect and summarize topology information (e.g., construct summary LSAs) describing their local OSPF/IS-IS area. Thereafter, the ABRs may distribute these summary LSAs to other ABRs on the backbone (e.g., to all other ABRs to which it is connected), thereby allowing the ABRs in external domains to develop a complete or partial topological understanding of the OSPF/IS-IS areas along the backbone. Depending on the network configuration, these summarized LSAs may or may not be distributed to internal nodes within the other OSPF/IS-IS routers).
Hence, while the prior art method reduces the number of LSAs that are flooded throughout the network, the fact remains that a localized link state distribution in one OSPF/IS-IS area (e.g., describing a change to an internal adjacency within the OSPF/IS-IS area) may lead to link state distributions to other areas, which may trigger routers in those other areas to re-calculate their OSPF or IS-IS routes, update their Routing Information Base (RIB) and Forwarding Information Base (FIB) tables, or take other actions that consume network resources (e.g., bandwidth and Central Process Unit (CPU) resources).
In an environment of multiple areas or domains, it requires the utilization of intermediate Path Computation Elements (PCEs) to facilitate inter-domain Link State Protocol (LSP) computation. However, PCEs make the network management become more complex. As such, a simple and efficient manner for addressing scalability/convergence problems in large networks is desired.